Recent Measurements Of Neutron Total Cross Sections On A Wide Range Of Targets From 5 To 600 Mev At Lansce

We have completed a new set of total cross section measurements, snd have measured approximately 36 additional samples. The goal of the new measurements was 1% statistical accuracy in 1% energy bins with systematic errors less than 1%. This was achieved for all but the smallest samples, for which the statistical accuracy was as large as 2% in 1% bins. However, the energy resolution is significantly better than this at low energies. The samples were: * The APT spallation target material: W * Medium-mass stmctural materials: Ti, V, Cr, Mn, Fe, Co, Ni * Actinides: Th, depleted U * Other materials for global optical model development: F, Mg, P, S, K, Y, Mo, In, Au, Hg, natural Pb * Separated isotopes of light nuclei: 6Li%, 7Li, 1°B, 11B, 13C, * Medium- and heavy-mass separated isotopes: {sup 54,56}Fe, {sup 182,183,184,186}W * Few-nucleon physics: H, D.

The measurement of 28O-Mev neutron cross sections of various nuclei is described. The neutron beam used results from 340-Mev protons in the 184-in. cyclotron striking a 2-in. Be target. The neutron detector consists of a double coincidence anthracene scintillation counter telescope which counts recoil protons scattered at 15 deg from a paraffin cylinder placed in the collimated neutron beam. A 2-in. Cu absorber placed between the counters assures that only protons of energy greater than 250 Mev are counted. The cross sections for all nuclei measured from Li to Pb are smaller than the corresponding cross sections measured at 90 Mev by factors between 0.5 and 0.6.

The Weapons Neutron Research Facility has been used to obtain moderate-resolution total neutron cross section data for H, C, 2°8Pb, 232Th, 238U, and 242Pu over the energy range 5 to 200 MeV. Neutrons were produced by bombarding a 2.5-cm diam by 15-cm long Ta target with an 800 MeV pulsed proton beam from LAMPF. A 10.2-cm diam by 15.2-cm thick NE110 proton recoil detector was used at a flight path of 32 meters, giving a time-of-flight resolution of 60 ps/m. The total cross section results are compared to ENDF/BV evaluations and to previous data where possible.